SODIUM CHLORIDE-BERTHOLLET'S LAWS 445 



Thus we now find ample confirmation from various quarters for the 

 following rules of Berthollet, applying them to double saline deconv 

 positions 1. From two salts MX and NY containing different haloids 

 and metals there result from their reaction two others, MY and NX, 

 but such a substitution will not proceed to the end unless one product 

 passes from the sphere of action. 2. This reaction is limited by the 

 existence of an equilibrium between MX, NY, MY, and NX, because a 

 reverse reaction is quite as possible as the direct reaction. 3. This limit 

 is determined both by the measure of the active affinities and by the rela- 

 tive masses of the substances as measured by the number of the reacting 

 molecules. 4. Other conditions being constant, the chemical action ia 

 proportional to the product of the chemical masses in action. 29 



standing its importance and the fact that the theoretical side of the subject (thanks 

 especially to Guldberg and Vau't Hoff) has since been rapidly pushed forward. If the re- 

 searches of Gustavson took account of the influence of mass, and were more fully 

 supplied with data concerniuglvelociti.es and temperatures, they would be very important, 

 because of the great significance which the case considered has for the understanding of 

 double saline decompositions in the absence of water. 



Furthermore, Gustavson showed that the greater the atomic weight of the element 

 (B, Si, Ti, As, Sn) combined with chlorine the greater the amount of chlorine replaced 

 by bromine by the action of CBr 4 , and consequently the less the amount of bromine 

 replaced by chlorine by the action of CC1 4 on bromine compounds. For instance, for 

 chlorine compounds the percentage of substitution (at the limit) is 



BC1 3 SiCl 4 TiCl 4 AsCl 5 SnCl 4 



10-1 12-5 48-6 71-8 77-5 



It should be observed, however, that Thorpe, on the basis of lus experiments, denies 

 the universality of this conclusion. I may mention one conclusion which it appears to me 

 may be drawn from the above-cited figures of Gustavson, if they are subsequently verified 

 even within narrow limits. If CBr 4 be heated with RC1 4 , then an exchange of the bromine 

 for chlorine takes place. But what would be the result if it were mixed with CC1 4 ? 

 Judging by the magnitude of the atomic weights, B = ll, C = 12, Si =28, about 11 p.c. o! 

 the chlorine would be replaced by bromine. But to what does this point ? I think that 

 this shows the existence of a motion ofthe atoms in the^molecule. The mixture of CC1 4 

 and CBr 4 does not remain in a condition of static equilibrium ; not only are the molecules 

 contained in it in a state of motion, but also the atoms in the molecules, and the above 

 figures show the measure of their translation under these conditions. The bromine ia 

 the CBr 4 is, within the limit, substituted by the chlorine of the CC1 4 in a quantity of 

 about 11 out of 100: that is, 'a portion of the atoms of bromine previously to this moment 

 in combination with one atom of carbon pass over to the other atom of carbon, and th* 

 chlorine passes over from this second atom of carbon to replace it. Therefore, also, in 

 the homogeneous mass CC^ all the atoms of Cl do not remain constantly combined with 

 the same atoms of carbon, and there is an exchange of atoms between different mole' 

 cules in a homogeneous medium also. This hypothesis may in my opinion explain 

 certain phenomena of dissociation, but though mentioning it I do not consider it worth 

 while to dwell upon it. I will only observe that a similar hypothesis suggested itself to 

 me in my researches on solutions, and that Pfauudler enunciated an essentially similar 

 hypothesis, and in recent times a like view is beginning to find favour with respect to the 

 electrolysis of saline solutions. 



89 Berthollet's doctrine is hardly at all affected in principle by showing that there are 

 cases in which there is no decomposition between salts, because the affinity may be so 



